Magnesium Slag Defects in Ductile Iron 1

Example of magnesium dross stringers.

Magnesium containing reaction products from ductile iron treatment are a potential source for inclusion defects in ductile iron. Your local Elkem team will assist you to choose the right MgFeSi alloys for your process and this will help in minimising these defects and thus reduce scrap rates.

Slag inclusions are typically found just beneath or at the cope surface as a result of improper separation during liquid metal processing. Magnesium slag defects may also arise from turbulent mould filling, and are often found as dross like stringers in areas of the casting where metal is deadlocked.

Possible causes:

• Inadequate slag separation from treatment vessel, metal processing and pouring systems.
• Insufficient time between treatment and pouring to let slags separate to the surface.
• Lack of slag traps or filter in the gating system.
• Low pouring temperature.
• High treatment temperature causing the need for elevated magnesium additions.
• Excessive base sulphur content causing the need for high magnesium additions.
• Excess addition of slag forming elements with alloys, such as Ca and Al.
• Turbulent mould filling.

The selection of the appropriate nodularisers and inoculants is critical to the elimination of slag related defects in ductile iron castings. Elkem is the market leader and produces the largest range of nodularisers with the tightest specifications. The product range of Elmag®, Lamet® and Remag® is designed to suit the vast majority of base metal and treatment conditions. In many cases these nodularisers can be tailor made to suit individual requirements.

The use of high quality nodulariser coupled with a low slag forming, high potency inoculant like Reseed® and Ultraseed®), and expert technical advice, will ensure that the iron going into each mould is clean and free from slag forming contaminants.